Gas turbine speed control



March 13, 1962 E. KUMM ET AL 3,025,036

GAS TURBINE SPEED CONTROL Filed Jan. 6, 1960 INVENTORS 2 EMERSON 1.. KUMM BY JOHN w. BLACK A TTOR NE Y5 United States Patent Oiiice 3,025,035 Patented Mar. 13, 1962 3,025,036 GAS TURBINE SPEED CONTROL Emerson L. Kumm, Phoenix, Ariz., and John W. Black,

Santa Barbara, Calif., assignors to Curtiss-Wright Corporation, a corporation of New Jersey Filed Jan. 6, 1960, Ser. No. 885 4 Claims. (Cl. 25359) This invention relates generally to gas turbines and more particular to an improved speed control device for such turbines.

Many devices for controlling or limiting the maximum possible speeds of gas turbines have been proposed and most turbines are normally equipped with such control devices. However, these devices are generally auxiliary systems and failure thereof can thus result in the turbine overspeeding to destruction with possible loss of life and property.

With the foregoing in mind, it is a primary object of the present invention to provide a novel speed control device for gas turbines which may be used in place of or as a supplement to conventional speed control devices for positively preventing overspeeding of the turbine.

More particularly, it is an object to provide a speed control device which includes a portion of the conventional turbine structure itself to the end that reliability of high order is achieved and to the further end that the control can be effected with minimum additional components whereby the possibility of failure is correspondingly minimized.

Another object is to provide a turbine speed control device which is actuated in response to an increase in the turbine speed above a given value in a completely automatic manner.

Briefly these and many other objects and advantages of this invention are attained by incorporating in a gas turbine novel mounting means for the stator blades normally receiving the discharging gas from the turbine blades. More particularly, the stator blades are individually rotatably mounted so that their angle of attack with respect to the direction of the discharge gas is varied when the blades themselves are rotated. Suitable stop means are provided for initially positioning the blades to provide a positive angle of attack for normal turbine operation. The blades are also biased to this position to avoid the possibility of any inadvertent or unintentional movement of the blades.

With the foregoing arrangement, an increase in turbine wheel velocity results in a decrease in the angle of attack between the discharging gas velocity vector and initial position of the stator blades. When this angle of attack is reduced to zero and becomes negative, a torque will be aerodynamically exerted on the stator blades rotating them to an overlapping relationship eifectively closing the same and thereby throttling the discharging gas. The turbine wheel consequently is slowed. The control system thus provides protection against overspeeding. In addition it can be employed as a primary speed control device.

A better understanding of the invention will be had by referring to one embodiment thereof as illustrated in the accompanying drawings, in which:

FIGURE 1 is an enlarged fragmentary plan View, partly in cross section, showing a portion of a turbine wheel together with gas nozzles and stator blades mounted in accordance with the invention;

FIGURE 2 is a fragmentary elevational view partly in cross section taken generally in the direction of the arrows 22 of FIGURE 1; and

FIGURE 3 shows velocity vector diagrams useful in explaining the operation of the invention.

Referring first to FIGURE 1, there is shown a portion of the periphery of a turbine wheel 10 including turbine blades 11. To one side of the turbine blades there are provided nozzles 12 for ejecting gas into the turbine blades as indicated by the arrows. On the opposite sides of the blades there is provided a stator wheel 13 including a plurality of stator blades 14 for receiving the discharging gas as also indicated by the arrows.

In accordance with the invention, each of the stator blades 14 is individually mounted for rotative movement about a pivot axis as indicated at 15 which, as illustrated, is disposed substantially closer, as measured along the blade chord, to the downstream edge of said stator blade than to its upstream edge. Rotation of the stator blades is effected simultaneously by suitable coupling means which may take the form of drive gears 16 secured to the stator blades respectively and intermediate idling or coupling gears 17 disposed therebetween.

With the foregoing arrangement, it will be evident that rotation of the driving gears 16 in a counter-clockwise direction as viewed in FIGURE 1 will result in rotation of the coupling gears 17 in a clockwise direction so that all of the stator blades will simultaneously be moved in a counter-clockwise or like directions. In the embodiment shown in FIGURE 1, the various stator blades 14 are shown in their full open or extreme clockwise position in solid lines. Rotation of the blades in a counterclockwise direction will result in their closing into overlapping relationship as indicated by the dotted lines. The overlapping engagement of the various blades serves as a stop for the maximum closed or counter-clockwise position.

The maximum open or solid line position in turn is controlled by a single stop 18 engaged by a bell crank 18' rigidly secured to one of the stator blades at its pivot point. Further, the blades are all biased to their open clockwise position by a spring 19 secured to the extreme lower end of one of the blades and to the stator wheel 13. Since all of the stator blades are ganged together by the various idling gears 17, only one stop means is necessary to check the clockwise or open extent of all of the blades and only one spring is necessary to bias all of the blades to such open position.

The above-described configuration can better be understood by reference to FIGURE 2 wherein the manner in which the blades 14 are rotatably mounted to the stator wheel rim 13 is shown. Also clearly shown is the bell crank 18 and stop 18 for the one of the stator blades incorporating this stop means. Preferably, the bell crank 18' itself may be rotationally positioned and then locked to the rotating shaft of the stator blade so that the maximum open position of the blades may be adjusted. This initial adjustment is such as to provide a positive angle of attack of the stator blades to the discharging gases from the outlets of each of the turbine blades 11 respectively. The pivot axis of each stator blade 11 is so disposed that, when the angle of attack of said discharging gases on said stator blades is positive, the pressure of said gases on the stator blades exerts a clockwise turning moment on said blades, as viewed in FIG. 1, thereby helping the spring 19 hold the stator blades 11 in their open position.

The operation of the turbine speed control can best be understood by now referring to the vector diagrams illustrated in FIGURE 3. For normal turbine speeds and with reference to the upper vector diagram, V, represents the turbine blade velocity and as shown extends to the left. V in turn represents the gas velocity from the nozzles 12 of FIGURE 1. Accordingly, the vector V will represent the gas velocity relative to the turbine blades. Similarly, the discharge velocity of the gases relative to the turbine blades is represented by the vector V and this same gas discharge velocity relative to the stator blades is represented by the vector V The angle with respect to the direction of movement of the turbine blades formed by the discharge gas vector V relative to the stator blades is indicated by the letter A. The initial or completely open position of each of the stator blades 14 is adjusted by adjusting the stop bell crank 18 so that the angle of attack of each of the stator blades with respect to the vector V is positive when the turbine wheel is operating at a normal speed.

Assume now that the turbine wheel increases its speed towards an overspeed condition. This situation is illustrated in the second vector diagram of FIGURE 3 wherein the increased turbine blade velocity is indicated by the elongated vector V In this diagram, the gas discharge velocity from the nozzle V is the same but asa consequence of the increased turbine speed, the gas velocity relative to the turbine blades is now represented by the shorter vector V Similarly, the discharge gas velocity relative to the turbine blades is represented by the vector V' and this discharge gas velocity relative to the stator blades is indicated by the vector V' It will be immediately noted that the original angle A of the discharging gas with respect to the direction of motion of the turbine blades has increased to the value A. This increased angle decreases the angle of attack of the discharging gas relative to the stator blades as shown in FIGURE 1 and thus decreases the aerodynamic pressure tending to hold the blades in their extreme clockwise position.

If the speed of the turbine blades V increased to a dangerous condition, the initial setting of the stator blades is such that the angle A will increase to such a value that the angle of attack on the stator blades will become negative. Then, because of the aforedescribed position of the pivot axis 15 of each stator blade 11, the aerodynamic pressure will establish a counter-clockwise turning moment on the stator blades moving them in a counterclockwise direction against the bias of the spring 1?. Once this initial movement is effected, the angle of attack becomes increasingly negative extremely rapidly so that the blades close relatively quickly into their dotted line overlapping position illustrated in FIGURE 1. Closure of the stator blades to this position, immediately throttles the discharging gas from the turbine blades with a consequent slowing down and stopping of the turbine wheel. The exiting gas leakage about the turbine blades will provide sufiicient pressure to hold the blades in their closed position. When the turbine is completely stopped and the gas velocity from the nozzles shut ofi, the spring 19 will return all of the blades to their normally open position shown in solid lines in FIGURE 1 and operation of the turbine can be resumed.

From the foregoing description, it Willbe evident that a degree of speed control of the turbine can be effected directly by positive positioning of the stator blades themselves. In other words, the stator blades can serve as a primary speed control means. Thus, the invention is applicable to conventional speed control of turbines as well as a safety device to provide overspeed control thereof.

It will also be evident from the foregoing description that the overspeed control is efiected with a minimum addition of components, the stator blades themselves serving dual functions of both guiding the discharging gas from the outlets of the turbine blades and also throttling the gas in the event of overspeeding of the turbine.

While only one embodiment of the invention has been shown and described, many modifications that fall clearly within the scope and spirit of the invention will occur to those skilled in the art. The speed control system is therefore not to be thought of as limited to the particular embodiment set forth merely for illustrative purposes.

Whatis claimed is: i

1. A gas turbine comprising a turbine wheel having a plurality of blades extending therefrom; means for supplying gases to said turbine wheel blades for driving the turbine Wheel; and means for controlling the speed of the turbine wheel; said speed control comprising a plurality of stator blades disposed in the path of the turbine discharge gases, means for rotatably supporting each stator blade so that the angle of attack of the turbine discharge gases on the stator blades is varied upon rotation of said blades, and stop means for limiting rotation of said stator blades toward a maximum open position with respect to flow of the turbine discharge gases therethrough, said stator blade rotatable supporting means being such that during operation of the turbine wheel below a predetermined speed the turbine discharge gases exert a turning moment on each stator blade urging said stator blade toward its said maximum open position and when the turbine wheel speed exceeds said predetermined speed the turbine discharging gases exert a turning moment in the opposite direction on said stator blades for rotating said stator blades toward a closed position with respect to said flow of turbine discharge gases.

2. A gas turbine as claimed in claim 1 and including spring means for urging said-stator blades toward their said maximum open position.

3. A gas turbine as claimed in claim 1 and in which said stop means is disposed so that when the turbine speed increases beyond said predetermined value the angle of attack of the turbine discharge gases on the stator blades reverses.

4. A gas turbine as claimed in claim 1 and in which said rotatable supporting means for each stator blade provides said blade with a pivot axis which is disposed substantially closer to the blade downstream edge than to its upstream edge and in which said stop means is disposed so that during turbine operation at speeds below said predetermined value said turbine discharge gases have a positive angle of attack on said stator blades and when the turbine speed exceeds said predetermined value said angle of attack becomes negative.

References Cited in the file ofthis patent UNITED STATES PATENTS 

